The present invention relates to a method for the adaptive control of operating parameters during the spark-erosive cutting of a workpiece in a spark-erosive cutting plant having pressure and/or suction scavenging of the work gap. The invention also relates to a spark-erosive cutting plant with a device for the pressure and/or suction scavenging of the work gap and adaptive control device for the control of operating parameters in accordance with the sensed instantaneous flow state of the scavenging medium in the work gap.
Such a method and apparatus are known from Swiss Pat. No. 548,256. In the known method and apparatus, operating parameters such as the scavenging medium flow quantity and the duration of the interval between the operating pulses are controlled or regulated as a function of the actual parameter values, to be considered as process quantities. The known method and apparatus permit a usable regulation of the manipulated variables for the operating parameters. However in the case of extreme cutting conditions, such as occur more frequently during the general technical development, the known method and apparatus are no longer adequate for ensuring optimum cutting conditions in all circumstances, so that there is a risk of wire breaks.
A wire break frequently results from the fact that the quantity of scavenging medium flowing through the work gap, e.g. deionized water, undergoes variations. A change to the scavenging medium flow rate through the work gap can result not only from fluctuations in the scavenging medium supply, but also can be due to varying cutting situations, particularly varying geometrical conditions, including varying scavenging cross-sections. A deterioration of the scavenging conditions can result if closely spaced contour elements appear in the cutting path; the cutting path comes into the vicinity of a starting bore; the workpiece surface has steps or shoulders; or there is a transition from a cylindrical cut into a three-dimensional cut. Unfavorable scavenging conditions are also obtained when cutting is begun from the outside of the workpiece.